With the recent trend toward a healthy life style and a growing demand for a preventive remedy of diseases, a number of research have been made on the health-improving functions of fish oils or components thereof such as icosapentaenoic acid (C20:5, which will hereinafter be abbreviated as “IPA”) and docosahexaenoic acid (C22:6, which will hereinafter be abbreviated as “DHA”). Specifically, anti-arteriosclerotic effects, cerebral function improving effects, visual function improving effects, antitumor effects and anti-inflammatory effects are known (Journal of Oleo Science, 48, 1017(1999) and the like).
These components have a strong rancid odor upon storage, so the practical application of an oil or fat composition containing such a component is therefore extremely limited for its flavor. In addition, it has been pointed out that IPA has inhibitory effects on platelet aggregation or abilities to prolong the bleeding time. (Atherosclerosis, 50, 3-10(1984), Lipids, 32, 1129-1136(1997)).
On the other hand, the present inventors have found that ω3 unsaturated monoglycerides-diglycerides including IPA and DHA have a body fat burning activity (JP2001-64672 A). They have also found that monoglycerides, especially IPA monoglycerides have high PPAR activating effects (JP2001-354558 A). But the PPAR activating effects of DHA monoglyceride remain to be elucidated.
The term “PPAR” as used herein means one of the nuclear receptors which is activated by a peroxisome proliferator (PPAR: Peroxisome Proliferator Activated Receptor). Recent studies have revealed that PPAR takes part in a number of physiological or pathological phenomena. Since fibrate compounds which are curative pharmaceuticals for hyperlipidemia and thiazolidine derivatives known for the treatment of diabetes were found to be PPAR agonists, attempts have been made to develop other new drugs for alleviating hyperlipidemia or insulin-resistant diabetes (The Cell, 31(6), 218-234(1999), J. Lipid Res. 37, 907-925(1996), Curr. Opin. Lipidol. 10, 151-159(1999)).
In addition, various technologies relating to monoglycerides have been disclosed. Preparation processes of monoglycerides are disclosed, for example, in JP-A-Hei 3-103499, JP-A-Hei 8-214892, JP-A-Hei 10-57086, JP2000-212588 A and JP2001-329291 A. In JP-A-Hei 7-39302, monoglycerides containing a highly unsaturated fatty acid are disclosed. These monoglycerides are nevertheless not satisfactory in their flavor.
In JP-A-Hei 8-60181 and JP-A-Hei 10-265795, oil or fat compositions containing partial glycerides including monoglycerides are disclosed. These compositions are composed mainly of diglycerides so that dispersibility in water is superior to those composed mainly of triglycerides. Owing to a low monoglycerides content, however, these compositions involve problems of processability, such as impossibility of incorporating water therein.
As described above, it has been elucidated that oil or fat compositions containing IPA or DHA have a variety of health functions. Yet they have problems of processability, flavor, and the like and technologies capable of overcoming these problems remain to be established.
From such viewpoints, there is a growing demand for the development of an oil or fat composition having good processability and flavor as a food, and having excellent physiological effects.